Photometric redshifts and intrinsic alignments: degeneracies and biases in 3$\times$2pt analysis

Abstract

We present a systematic study of cosmological parameter bias in weak lensing and large-scale structure analyses for upcoming imaging surveys induced by the interplay of intrinsic alignments (IA) and photometric redshift (photo-z) model mis-specification error. We first examine the degeneracies between the parameters of the Tidal Alignment - Tidal Torquing (TATT) model for IA and of a photo-z model including a mean shift ($\Delta \bar{z}$) and variance (${\sigma }_z$) for each tomographic bin of lenses and sources, under a variety of underlying true IA behaviors. We identify strong degeneracies between: (1) the redshift scaling of the tidal alignment amplitude and the mean shift and variances of source bins, (2) the redshift scaling of the tidal torquing amplitude and the variance of the lowest-$z$ source bin, and (3) the IA source density weighting and the mean shift and variance of several source bins. We then use this information to guide our exploration of the level of cosmological parameter bias which can be induced given incorrect modelling of IA, photo-z, or both. We find that marginalizing over all the parameters of TATT is generally sufficient to preclude cosmological parameter bias in the scenarios we consider. However, this does not necessarily mean that IA and photo-z parameters are themselves unbiased, nor does it mean that the best-fit model is a good fit to the data. We also find scenarios where the inferred parameters produce ${\chi }_{\mathrm{DOF}}^2$ values indicative of a good fit but cosmological parameter bias is significant, particularly when the IA source density weighting parameter is not marginalized over.

20 pages, 13 figures. Updated to match accepted version

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Cited by in corpus (7)

• The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics
• Dark Energy Survey Year 3: Blue Shear
• Euclid and KiDS-1000: Quantifying the impact of source-lens clustering on cosmic shear analyses
• A rising tide: Intrinsic alignments since the turn of the millennium
• 6x2pt: Forecasting gains from joint weak lensing and galaxy clustering analyses with spectroscopic-photometric galaxy cross-correlations
• Impact of Large-Scale Structure Systematics on Cosmological Parameter Estimation
• Non-linear infusion of intrinsic alignment and source clustering: impact on non-Gaussian cosmic shear statistics